Hybrid power control for a power amplifier

ABSTRACT

A hybrid power control system ( 102 ) that selectively applies voltage-based gain control and current-based gain control and method ( 300 ) of controlling a power amplifier ( 104 ) gain are presented. A voltage-based gain control signal ( 120 ) is applied to control the gain of the power amplifier when a level output power is indicated by a power contour signal ( 132 ). Whether the power amplifier is saturated is identified. A current-based gain control signal ( 122 ) is applied to control the gain of the power amplifier when the power amplifier is saturated and a decrease in output power is indicated by the power contour signal.

TECHNICAL FIELD

The present invention generally relates to power amplifiers and, moreparticularly, to power level control in power amplifiers.

BACKGROUND

Power amplifiers are typically used to increase the power level of anelectrical signal. The relationship between the input power and theoutput power of a power amplifier is generally referred to as the“transfer function” of the power amplifier, and the magnitude of thetransfer function is referred to as “gain.” Radio frequency (RF) poweramplifiers oftentimes implement a gain control architecture that can beused to vary amplifier gain, and thus RF signal output power, for powerleveling purposes.

In a voltage controlled power amplifier, gain control is typicallyimplemented by detecting the voltage level of the power amplifier's RFoutput signal and comparing that voltage level to a reference signal. Ina current controlled power amplifier, gain control is typicallyimplemented by detecting the current level of the RF output signal andcomparing that current level to a reference signal. Voltage-based gaincontrol typically provides accurate control over the power amplifier'spower leveling characteristics, even when variations in voltage standingwave ratio (VSWR) and output voltage occur. In contrast, current-basedgain control typically exhibits poor power leveling characteristics whenVSWR and output voltage vary.

There are disadvantages to using voltage-based gain control, however.For example, if a voltage controlled power amplifier is amplifying atime division multiple access (TDMA) signal, the power amplifiertypically will ramp up power to transmit in allocated time slots (i.e.on specific channels), and then ramp down power in time slots allocatedto other systems. If saturation occurs during this process, transientadjacent channel power (ACP) is oftentimes generated by the poweramplifier. Transient ACP is known to adversely interfere withcommunication signals on adjacent TDMA channels. This phenomenon iscommonly referred to as “splattering.”

BRIEF DESCRIPTION OF THE DRAWINGS

Preferred embodiments will be described below in more detail, withreference to the accompanying drawings, in which:

FIG. 1 depicts a power amplification system that is useful forunderstanding the present invention;

FIG. 2 depicts a timing signal diagram that is useful for understandingthe present invention; and

FIG. 3 depicts a flowchart presenting a method of controlling a gain ofa power amplifier, which is useful for understanding the presentinvention.

DETAILED DESCRIPTION

While the specification concludes with claims defining features of theinvention that are regarded as novel, it is believed that the inventionwill be better understood from a consideration of the description inconjunction with the drawings. As required, detailed embodiments of thepresent invention are disclosed herein; however, it is to be understoodthat the disclosed embodiments are merely exemplary of the invention,which can be embodied in various forms. Therefore, specific structuraland functional details disclosed herein are not to be interpreted aslimiting, but merely as a basis for the claims and as a representativebasis for teaching one skilled in the art to variously employ thepresent invention in virtually any appropriately detailed structure.Further, the terms and phrases used herein are not intended to belimiting but rather to provide an understandable description of theinvention.

Arrangements described herein relate to a hybrid power control systemfor controlling a gain of a power amplifier, for example a radiofrequency (RF) power amplifier. The hybrid power control system cancontrol the gain of the power amplifier both by detecting the voltage ofthe output signal generated by the power amplifier, and by detecting thecurrent of the output signal. For example, when the output power of theamplifier is to be increased, or ramped, voltage-based gain control canbe used to control the gain by monitoring the voltage of the outputsignal. As noted, voltage-based gain control can be used to provideaccurate control over the amplifier's output characteristics, even whenvariations in voltage standing wave ratio (VSWR) and output voltageoccur.

If saturation is detected in the amplifier, however, and thus it isdesired to reduce the gain of the amplifier, current-based gain controlcan be implemented. In contrast to voltage-based gain control,current-based gain control can be used to control the gain of the poweramplifier by monitoring the current of the output signal, and can do sowithout generating significant levels of transient adjacent channelpower (ACP). Accordingly, signal degradation on adjacent TDMA channelsdue to transient ACP can be minimized.

FIG. 1 depicts a power amplification system (hereinafter “system”) 100that is useful for understanding the present invention. The system 100can include a hybrid power control system 102 and a gain controlledpower amplifier (hereinafter “power amplifier”) 104 that amplifies aninput signal 106. In one arrangement, the input signal 106 can be an RFinput signal, although the invention is not limited in this regard.Indeed, the input signal 106 can be an audio signal, or any otherelectrical signal for which power amplification is desired. The gain ofthe power amplifier 104 can be controlled by applying to the poweramplifier 104 a gain control signal 108 generated by the hybrid powercontrol system 102.

The hybrid power control system 102 can include a switch 110, avoltage-based gain control circuit 112, a current-based gain controlcircuit 114, and a saturation detection circuit 116. The switch 110 canselect the gain control signal 108 from one or more available gaincontrol signals. For example, the switch 110 can selectively change asignal input path 118 between the voltage-based gain control circuit112, which generates a voltage-based gain control signal 120, and thecurrent-based gain control circuit 114, which generates a current-basedgain control signal 122. Operation of the switch 110 can be controlledby the saturation detection circuit 116, as will be described herein ingreater detail.

Optionally, additional components also can be provided to amplify,condition, or otherwise process the gain control signal 108. Forexample, a pre-amplifier 124 can be provided to amplify the gain controlsignal 108 before the gain control signal 108 is input into the poweramplifier 104. Further, active or passive filters, for example acapacitor 126, can be provided to filter transient surges that may begenerated by the switch 110 during the switching process. It should benoted, however, that a myriad of otheramplification/conditioning/processing components can be used and theinvention is not limited to these specific examples.

The voltage-based gain control circuit 112 can include a logarithmicamplifier 128. The logarithmic amplifier 128 can generate thevoltage-based gain control signal 120 represented by the followingequation:

$V_{out} = {K\;\ln\;\frac{V_{i}}{V_{pc}}}$where V_(i) is a voltage of an input signal 130, V_(pc) is a voltage ofa power contour signal 132, and K is a constant. The constant K can beselected to achieve a desired gain, for example using suitable passiveand/or active electronic components (not shown). Logarithmic amplifiergain selection is well known to those skilled in the art.

In an alternate arrangement, a difference amplifier, which also is wellknown in the art, can be implemented within the hybrid power controlsystem 102 in lieu of the logarithmic amplifier 128.

In the present example, the power contour signal 132 can be a signalthat indicates a desired characteristic of an output signal 134generated by the power amplifier 104. The desired characteristic can be,for example, a desired output power or a desired output voltage, forinstance in accordance with a desired power modulation scheme, as willbe described. For brevity, the term “output power” will be used in theexamples described herein, but one skilled in the art will appreciatethat the invention is not limited in this regard.

The input signal 130 can be generated from the output signal 134 of thepower amplifier 104, thereby configuring the voltage-based gain controlcircuit 112 as a closed loop control circuit. For example, a coupler 136can be provided between the power amplifier and a load, such as anantenna 138, to couple the output signal 134 of the power amplifier 104to the logarithmic amplifier 128. In one arrangement, the coupler 136can directly connect the output signal 134 of the power amplifier 104 tothe logarithmic amplifier 128 as the input signal 130. In anotherarrangement, the coupler can include voltage sensing components thatgenerate the input signal 130 from the power amplifier output signal134. Such components are well known in the art.

The gain of the logarithmic amplifier 128 can be selected to achieve avoltage-based gain control signal 120 having desired characteristics forvoltage-based gain control of the power amplifier 104. In that regard,the gain of the logarithmic amplifier 128 also can be selected tocompensate for any gain or attenuation that may result from use of thecoupler 136 to generate the input signal 130 from the output signal 134of the power amplifier 104.

The current-based gain control circuit 114 can include a current sensor140 that detects the current level of the output signal 134 generated bythe power amplifier 104, and generates a current signal 142 thatcorresponds to the detected current level. For instance, the voltage ofthe current signal 142 can correspond to the detected current level. Thecurrent sensor 140 can comprise a voltage probe, a voltage dividercircuit, or any other components suitable for sensing current.

The current-based gain control circuit 114 also can include a comparator144. A voltage supply signal 146 can be provided as a positive voltagesupply to the comparator 144 in order to tune the current-based gaincontrol signal 122. The voltage supply signal 146 can be suitablyselected so as to ensure that when the switch 110 switches from thevoltage-based gain control signal 120 to the current-based gain controlsignal 122, the voltage levels from the voltage-based gain controlsignal 120 and the current-based gain control signal 122 are at leastapproximately the same. In particular, use of the voltage supply signal146 as the positive supply voltage for the comparator 144 can cap theoutput of the comparator 144 to the voltage of the voltage supply signal146. For example, when the voltage of the power contour signal 132 isgreater than the voltage of the current signal 142, the output of thecomparator 144 will be approximately equal to the voltage of the voltagesupply signal 146.

Switching from the voltage-based gain control signal 120 to thecurrent-based gain control signal 122 in this manner can minimizediscontinuities in the gain control signal 108 during transition fromthe voltage-based control to the current-based control. Any remainingdiscontinuities that may be present in the gain control signal 108 canbe smoothed by the capacitor 126 (or other suitable signal conditioningcomponents). Thus, the use of a voltage supply signal 146 as thepositive supply voltage input to the comparator 144 can prevent, or atleast minimize, adverse effects that may otherwise result from suchdiscontinuities.

In one arrangement, the voltage supply signal 146 can be generated bysampling the gain control signal 108 using a peak and hold detector 148that suitably samples the gain control signal 108 and generates thevoltage supply signal 146 that corresponds to the measured gain controlsignal samples. Thus, use of the peak and hold detector 148 provides ameans of ensuring that the voltage supply signal 146 is adjusted to theproper voltage level to ensure that the voltage of the current-basedgain control signal 122 is approximately equal to the voltage of thevoltage-based gain control signal 120 when switching betweenvoltage-based gain control and current based gain control occurs. Othercomponents, for example application specific integrated circuits(ASICs), may be suitable for generating the voltage supply signal,however, and such components are within the scope of the presentinvention.

The current sensor 140 can output the current signal 142 to thecomparator 144, which can compare the current signal 142 to the powercontour signal 132 and generate the current-based gain control signal122. The current-based gain control signal 122 can indicate whether thecurrent signal 142 or the power contour signal 132 is larger. Forexample, in an arrangement in which the power contour signal 132 isprovided to the non-inverting input of the comparator 144 and thecurrent signal 142 is input into the inverting input of the comparator144, if the voltage of the power contour signal 132 is greater than thevoltage of the current signal 142, the voltage of the current-based gaincontrol signal 122 can be approximately equal to the positive supplyvoltage of the comparator 144. If, however, the voltage of the powercontour signal 132 is less than the voltage of the current signal 142,the voltage of the current-based gain control signal 122 can beapproximately equal to the negative supply voltage of the comparator144, for example 0 V. In one arrangement, the voltage supply signal 146can be adjustable, and may be adjusted to calibrate the current-basedgain control circuit 114, as will be described.

Further, the comparator 144 may be configured to not only compare thepower contour signal 132 to the current signal 142, but to also filterthe output signal to achieve a desired frequency response. For instance,if the input signal 106 is limited to a particular range of frequencies,additional passive and/or active electronic components (not shown) canbe provided in the comparator circuit to implement pass band filtering.Alternatively, a separate filter can be used. Implementation of suchsignal filtering techniques is well known to those skilled in the art.

As noted, the switch 110 can select between the voltage-based gaincontrol circuit 112 and the current-based gain control circuit 114 toprovide the gain control signal 108 to the power amplifier 104, andoperation of the switch 110 can be controlled by the saturationdetection circuit 116. In one arrangement, the saturation detectioncircuit 116 can include a comparator 150 and a set/reset latch 152. Thecomparator 150 can compare the gain control signal 108 to a voltagereference signal 154 and generate a saturation indication signal 156which indicates whether the power amplifier 104 is saturated based uponwhether the gain control signal 108 or the voltage reference signal 154is larger.

For example, if the voltage of the gain control signal 108 is greaterthan the voltage of the voltage reference signal 154, the voltage of thesaturation indication signal 156 can be approximately equal to thepositive supply voltage of the comparator 150. If, however, the voltageof the gain control signal 108 is less than the voltage of the voltagereference signal 154, the voltage of the saturation indication signal156 can be approximately equal to the negative supply voltage of thecomparator 150, for example 0 V. In this arrangement, the voltagereference signal 154 can be set to a voltage level that corresponds tothe voltage level of the gain control signal 108 when the poweramplifier 104 is saturated. Again, the voltage reference signal 154 canbe adjustable, and may be adjusted to calibrate detection of poweramplifier saturation, as will be described.

In another arrangement, rather than comparing the gain control signal108 to the voltage reference signal 154, the comparator 150 can compareanother signal, for example the power amplifier output signal 134, tothe voltage reference signal 154 in order to generate the saturationindication signal 156. In this arrangement, the voltage reference signal154 can be set to a voltage level that corresponds to the voltage levelof the power amplifier output signal 134 when the power amplifier 104 issaturated.

The comparator 150 can communicate the saturation indication signal 156to the set/reset latch 152. The set/reset latch 152 can process thesaturation indication signal 156, along with at least one latch timingsignal, for instance a latch timing set signal 158, to generate a switchcontrol signal 162 that controls operation of the switch 110.Optionally, a second latch timing signal, for example a latch timingreset signal 160, also can be processed to generate the switch controlsignal 162. The latch timing set signal 158 and/or the latch timingreset signal 160 can indicate the present state of the power contoursignal 132, for example when the amplitude of the power contour signal132 is increasing or decreasing. The latch timing set/reset signals 158,160 also can indicate when the amplitude of the power contour signal 132is maintained high or maintained low.

The latch timing set signal 158 and/or the latch timing reset signal 160can be generated from the power contour signal 132, for example using aset/reset signal generator 164. The set/reset signal generator 164 cancomprise one or more voltage detectors, comparators and/or othercircuits suitable for generating the set/reset signals. One or morevoltage reference signals (not shown) also can be provided to theset/reset signal generator 164.

Referring to FIG. 2, a signal timing diagram 200 is depicted thatpresents examples of the power contour signal 132, the latch timing setsignal 158 and the latch timing reset signal 160. At time T₁ the powercontour signal 132 can begin to increase (e.g. ramp up) from an initialvoltage V_(o), which can be low, to a high voltage V₁. The initialvoltage V_(o) can be, for instance, 0 V and the high voltage V₁ can be avoltage suitable for achieving the desired maximum output power from thepower amplifier. Thus, the period from time T₁ until time T₂ canindicate an output power increase, or ramp up.

At time T₂ the power contour signal 132 can reach the voltage V₁. Fromtime T₂ until time T₃, the high voltage V₁ can be maintained.Accordingly, the period from time T₂ until time T₃ can indicate a leveloutput power. At time T₃ the power contour signal 132 can begin todecrease (e.g. ramp down) from the high voltage V₁ to initial voltageV₀, reaching the V_(o) at time T₄. Thus, the period from time T₃ untiltime T₄ can indicate an output power decrease, or ramp down. The powercontour signal 132 can maintain the initial voltage V_(o) until time T₅.The period from time T₄ until time T₅ can indicate that low or zerooutput power be maintained. At time T₅ the cycle can repeat and continuethrough times T₆, T₇, T₈, and so on.

As noted, the latch timing set/reset signals 158, 160 can be generatedfrom the power contour signal 132. For the latch timing set/resetsignals 158, 160, the corresponding voltage levels are indicated as lowand high. The actual voltage levels represented by low and high are notcritical so long as the set/reset latch is able to recognize and processtransitions of the latch timing set/reset signals 158, 160 from low tohigh and from high to low.

At time T₁, the latch timing set signal 158 and the latch timing resetsignal 160 can transition from low to high. Alternatively, the latchtiming set signal 158 can transition from low to high at time T₁, andthe latch timing reset signal 160 can transition from low to high attime T₂. At time T₃, the latch timing set signal 158 can transition fromhigh to low. The latch timing reset signal 160 can transition from highto low at time T₄. Again, the cycles can repeat and continue throughtimes T₅, T₆, T₇, T₈, and so on. In another arrangement, the respectivevoltage levels can be reversed. For example, the latch timing set signal158 can be low from time T₁ to time T₃, high from time T₃ to time T₅,and so on. Similarly, the latch timing reset signal 160 can low fromtime T₁ to time T₄, high from time T₄ to time T₅, and so on.

Reference now should be made both to FIG. 1 and FIG. 2. When the powercontour signal 132 indicates to increase the output power of the poweramplifier 104 (e.g. ramp up output power) at time T₁, if the switch 110does not already connect the signal input path 118 to the voltage-basedgain control circuit 112, the transition of the latch timing set signal158 and/or the transition of the latch timing reset signal 160 at timeT₁ can trigger the set/reset latch 152 to connect the signal input path118 to the voltage-based gain control circuit 112. Accordingly, thevoltage-based gain control signal 120 can be used as the gain controlsignal 108 to provide voltage-based gain control of the power amplifier104 during the period from time T₁ to time T₃ (e.g. during power ramp upand while level output power is desired).

In an alternative arrangement, the transition of the latch timing setsignal 158 and/or the transition of the latch timing reset signal 160 attime T₂ can trigger the set/reset latch 152 to connect the signal inputpath 118 to the voltage-based gain control circuit 112. In such anarrangement, either voltage-based gain control or current-based gaincontrol can be used to control the gain of the power amplifier 104 whenoutput power is increased from time T₁ to time T₂, but the voltage-basedgain control signal 120 can be used as the gain control signal 108 toprovide voltage-based gain control of the power amplifier 104 during theperiod from time T₂ to time T₃ (e.g. while level output power isdesired).

At time T₃, the latch timing set signal 158 can transition from high tolow to indicate that the power contour signal 132 is indicating todecrease the output power of the power amplifier 104 (e.g. ramp downoutput power). If the saturation indication signal 156 indicates thatthe power amplifier 104 is not saturated when the power contour signal132 indicates to decrease power, the set/reset latch 152 can maintainthe switch 110 in its present state, thus keeping the signal input path118 connected to the voltage-based gain control circuit 112.

If, however, the saturation indication signal 156 indicates that thepower amplifier 104 is saturated when the power contour signal 132indicates to decrease output power, the set/reset latch 152 can controlthe switch 110 to connect the signal input path 118 to the current-basedgain control circuit 114. Thus, the current-based gain control signal122 can be used as the gain control signal 108 to provide current-basedgain control of the power amplifier 104 when output power is decreasingfrom time T₃ to time T₄. Accordingly, transient ACP that may otherwisebe generated if the voltage-based gain control circuit 112 were to beused to provide gain control when the power amplifier 104 is saturatedand the output power is being decreased.

In one arrangement, at time T₄ the latch timing reset signal 160 cantransition from high to low to indicate that the power contour signal132 is low. If the signal input path 118 is connected to thecurrent-based gain control circuit 114, and the saturation indicationsignal 156 indicates that the power amplifier 104 is no longersaturated, the set/reset latch 152 can control the switch 110 to connectthe signal input path 118 to the voltage-based gain control circuit 112.The set/reset latch 152 can maintain the switch 110 in that state untilpower amplifier saturation is again detected and an output powerdecrease is indicated.

In an alternate arrangement in which the latch timing reset signal 160is not used, but the current-based gain control circuit 114 was used toprovide gain control for output power increase from time T₃ to time T₄,the signal input path 118 can remain connected to the current-based gaincontrol circuit 114 until time T₅ (or time T₆). At time T₅ (or time T₇)the transition of the latch timing set signal 158 can indicate to theset/reset latch 152 to control the switch 110 to connect the signalinput path 118 to the voltage-based gain control circuit 112.

Now that operation of the hybrid power control system 102 has beendescribed, calibration of the voltage supply signal 146 and the voltagereference signal 154 will be described. To calibrate the voltage supplysignal 146, the voltage supply signal 146 can be set to 0 V. Inaddition, the power contour signal 132 can be input into the logarithmicamplifier 128 and the comparator 144. The voltage-based gain controlsignal 120 and the current-based gain control signal 122 also can begenerated. The latch timing set signal 158 for at least one cycle can besent to the set/reset latch 152, and the latch timing reset signal 160can be set to high. Under these conditions, the set/reset latch 152 canset the switch to select the current-based gain control circuit 114. Thevoltage supply signal 146 then can be adjusted until the voltage of thepower amplifier output signal 134 reaches a desired voltage level for agiven voltage level of the power contour signal 132.

To calibrate the voltage reference signal 154, an input signal 106 thatis level, or steady state, can be applied to the power amplifier 104. Inaddition, the gain control signal 108 that may be selectively varied andapplied to the pre-amplifier 124, or directly to the power amplifier 104if the pre-amplifier 124 is not used in the system 100. The voltage ofthe power amplifier output signal 134, the input signal 106, and thegain control signal 108 can be measured while the gain control signal108 is increased from a desired initial value. Further, the voltageratio of the output voltage of the power amplifier 104 to the voltage ofthe gain control signal 108 can be monitored. When the voltage ratiodecreases by a determined percentage, for example 10%, the poweramplifier can be determined to be saturated. The voltage of the gaincontrol signal 108 then can be measured when, or just before, saturationis detected, and the voltage reference signal 154 can be set to thatvoltage value.

FIG. 3 depicts a flowchart presenting a method 300 of controlling a gainof a power amplifier, which is useful for understanding the presentinvention. At step 302 a voltage-based gain control signal and acurrent-based gain control signal can be generated. At step 304, atleast one signal that indicates a present state of a power contoursignal can be generated. Referring to decision box 306, if there is anincreasing or a level output power indicated by a power contour signal,at step 308 a voltage-based gain control signal can be applied tocontrol gain of the power amplifier. Otherwise, the method 300 canproceed to step 310.

At step 310, whether the power amplifier is saturated can be identified,and a corresponding saturation indication signal can be generated. Atdecision box 312, a determination can be made as to whether the poweramplifier is saturated and a decreasing output power is indicated by apower contour signal. If so, at step 314 a current-based gain controlsignal can be applied to control the gain of the power amplifier.Otherwise, the method 300 can proceed to step 308. The method 300 cancontinue while gain control of the power amplifier is desired.

The flowchart and block diagrams in the figures illustrate thearchitecture, functionality, and operation of possible implementationsof systems, methods and computer program products according to variousembodiments of the present invention. In this regard, each block in theflowchart or block diagrams may represent a module, segment, or portionof code, which comprises one or more executable instructions forimplementing the specified logical function(s). It should also be notedthat, in some alternative implementations, the functions noted in theblock may occur out of the order noted in the figures. For example, twoblocks shown in succession may, in fact, be executed substantiallyconcurrently, or the blocks may sometimes be executed in the reverseorder, depending upon the functionality involved.

As above, any portion of the flowchart may be implemented as a computerprogram product for use with a computer system. Such implementations mayinclude a series of computer instructions fixed either on a tangiblemedium, such as a computer readable medium (e.g., a diskette, CD-ROM,ROM, or fixed disk) or transmittable to a computer system, via a modemor other interface device, such as a communications adapter connected toa network over a medium. The medium may be either a tangible medium(e.g., optical or analog communications lines) or a medium implementedwith wireless techniques (e.g., microwave, infrared or othertransmission techniques). The series of computer instructions embodiesall or part of the functionality previously described herein withrespect to the system. Those skilled in the art should appreciate thatsuch computer instructions can be written in a number of programminglanguages for use with many computer architectures or operating systems.Furthermore, such instructions may be stored in any memory device, suchas semiconductor, magnetic, optical or other memory devices, and may betransmitted using any communications technology, such as optical,infrared, microwave, or other transmission technologies. It is expectedthat such a computer program product may be distributed as a removablemedium with accompanying printed or electronic documentation (e.g.,shrink wrapped software), preloaded with a computer system (e.g., onsystem ROM or fixed disk), or distributed from a server or electronicbulletin board over the network (e.g., the Internet or World Wide Web).Of course, some embodiments of the invention may be implemented as acombination of both software (e.g., a computer program product) andhardware. Still other embodiments of the invention are implemented asentirely hardware, or entirely software (e.g., a computer programproduct).

The terms “a” and “an,” as used herein, are defined as one or more thanone. The term “plurality,” as used herein, is defined as two or morethan two. The term “another,” as used herein, is defined as at least asecond or more. The terms “including” and/or “having,” as used herein,are defined as comprising (i.e. open language).

Moreover, as used herein, ordinal terms (e.g. first, second, third,fourth, fifth, sixth, seventh, eighth, ninth, tenth, and so on)distinguish one message, signal, item, object, device, system,apparatus, step, process, or the like from another message, signal,item, object, device, system, apparatus, step, process, or the like.Thus, an ordinal term used herein need not indicate a specific positionin an ordinal series. For example, a process identified as a “secondprocess” may occur before a process identified as a “first process.”Further, one or more processes may occur between a first process and asecond process.

The Abstract of the Disclosure is provided to allow the reader toquickly ascertain the nature of the technical disclosure. It issubmitted with the understanding that it will not be used to interpretor limit the scope or meaning of the claims. In addition, in theforegoing Detailed Description, it can be seen that various features aregrouped together in various embodiments for the purpose of streamliningthe disclosure. This method of disclosure is not to be interpreted asreflecting an intention that the claimed embodiments require morefeatures than are expressly recited in each claim. Rather, as thefollowing claims reflect, inventive subject matter lies in less than allfeatures of a single disclosed embodiment. Thus the following claims arehereby incorporated into the Detailed Description, with each claimstanding on its own as a separately claimed subject matter.

This invention can be embodied in other forms without departing from thespirit or essential attributes thereof. Accordingly, reference should bemade to the following claims, rather than to the foregoingspecification, as indicating the scope of the invention.

1. A method of controlling a gain of a power amplifier, the methodcomprising: applying a voltage-based gain control signal to control thegain of the power amplifier when a level output power of the poweramplifier is indicated by a power contour signal; identifying whetherthe power amplifier is saturated; and applying a current-based gaincontrol signal to control the gain of the power amplifier when the poweramplifier is saturated and a decrease in output power is indicated bythe power contour signal.
 2. The method of claim 1, further comprising:applying the voltage-based gain control signal to the power amplifierwhen an increase in output power is indicated by a power contour signal.3. The method of claim 1, further comprising: based on the power contoursignal and the identification of whether the power amplifier issaturated, selectively controlling operation of a switch to selectbetween the voltage-based gain control signal and the current-based gaincontrol signal.
 4. The method of claim 1, wherein identifying whetherthe power amplifier is saturated comprises: comparing to a voltagereference signal at least one signal selected from a group consisting ofthe voltage-based gain control signal, the current-based gain controlsignal, and an output signal of the power amplifier.
 5. The method ofclaim 1, further comprising: generating at least one signal thatindicates a present state of the power contour signal; and generating atleast one saturation indication signal indicating whether the poweramplifier is saturated.
 6. The method of claim 1, further comprising:detecting a current level of an output signal generated by the poweramplifier; and comparing the current level to the power contour signalto generate the current-based gain control signal.
 7. The method ofclaim 1, further comprising: detecting a voltage level of an outputsignal generated by the power amplifier; and comparing the voltage levelto the power contour signal to generate the voltage-based gain controlsignal.
 8. The method of claim 1, further comprising: responsive toapplying the current-based gain control signal, determining whether thepower contour signal indicates an increase in or level output power; andapplying the voltage-based gain control signal to control the gain ofthe power amplifier when the increase in or level output power isindicated by the power contour signal.
 9. A method of controlling a gainof a power amplifier, the method comprising: generating a voltage-basedgain control signal; generating a current-based gain control signal;identifying whether the power amplifier is saturated; applying thevoltage-based gain control signal to control the gain of the poweramplifier when an increase in output power or a level output power ofthe power amplifier is indicated by a power contour signal; and applyingthe current-based gain control signal to control the gain of the poweramplifier when the power amplifier is saturated and a decrease in outputpower is indicated by the power contour signal.
 10. The method of claim9, further comprising: detecting current and voltage levels of an outputsignal generated by the power amplifier; comparing the current level tothe power contour signal to generate the current-based gain controlsignal; and comparing the voltage level to the power contour signal togenerate the voltage-based gain control signal.
 11. The method of claim9, further comprising: generating at least one latch timing signal thatindicates a present state of the power contour signal; and generating atleast one saturation indication signal indicating whether the poweramplifier is saturated.
 12. A hybrid power control system comprising: avoltage-based gain control circuit that generates a voltage-based gaincontrol signal; a current-based gain control circuit that generates acurrent-based gain control signal; a saturation detection circuit thatidentifies whether a power amplifier is saturated; and a switch thatapplies the voltage-based gain control signal to control a gain of thepower amplifier when an increase in output power of the power amplifieris indicated by a power contour signal and applies the current-basedgain control signal to control the gain of the power amplifier when thepower amplifier is saturated and a decrease in output power is indicatedby the power contour signal.
 13. The hybrid power control system ofclaim 12, wherein the switch applies the voltage-based gain controlsignal to the power amplifier when a level output power is indicated bya power contour signal.
 14. The hybrid power control system of claim 12,wherein the saturation detection circuit controls operation of theswitch to selectively apply the voltage-based gain control signal andthe current-based gain control signal to control the gain of the poweramplifier.
 15. The hybrid power control system of claim 12, wherein thesaturation detection circuit detects whether the power amplifier issaturated by comparing to a voltage reference signal at least one signalselected from a group consisting of the voltage-based gain controlsignal, the current-based gain control signal, and an output signal ofthe power amplifier.
 16. The hybrid power control system of claim 12,wherein the saturation detection circuit generates at least one signalthat indicates a present state of the power contour signal and generatesat least one saturation indication signal indicating whether the poweramplifier is saturated.
 17. The hybrid power control system of claim 12,wherein the saturation detection circuit generates at least one signalthat indicates the present state of the power contour signal.
 18. Thehybrid power control system of claim 12, wherein the current-based gaincontrol circuit comprises: a current sensor that detects a current levelof an output signal generated by the power amplifier; and a comparatorthat compares the current level to the power contour signal to generatethe current-based gain control signal.
 19. The hybrid power controlsystem of claim 12, wherein the current-based gain control circuitdetects a voltage level of an output signal generated by the poweramplifier and compares the voltage level to the power contour signal togenerate the voltage-based gain control signal.
 20. The hybrid powercontrol system of claim 12, wherein: responsive to the switch applyingthe current-based gain control signal to control the gain of the poweramplifier, the saturation detection circuit determines whether the powercontour signal indicates a level output power or an increase in outputpower; and the switch applies the voltage-based gain control signal tocontrol the gain of the power amplifier when the level or increase inoutput power is indicated by the power contour signal.